Process for improving the surface adhesion of shaped articles made from polyesters

ABSTRACT

This invention relates to a process for modifying the surface of a shaped article made from a polyester which comprises treating the article with an aqueous solution containing a halogenated fatty acid, a wetting agent and a polymer which is compatible with the halogenated fatty acid, and drying the treated article.

IJnited States Patent Seibel et a1.

1 H IMarch 13, 1973 PROCESS FOR IMPROVING THE SURFACE ADHESION 0F SHAPEDARTICLES MADE FROM POLYESTERS Inventors: Markus Seibel, Mainz; KlausThoese, Wiesbaden-Schierstein, both of Germany Assignee: KalleAktiengesellschait,

Wiesbaden-Biebrich, Germany Filed: April 22, 1968 Appl. No.2 723,265

Foreign Application Priority Data April 25, 1967 Germany .,.l( 62108U.S. Cl. ,.1l7/l38.8 F,117/73, 117/76 F, 117/161 UA, 117/161 UB, 117/161UE, 117/161 UF Int. Cl ..B32b 27/08, B44d 5/04 Field of Search...1l7/138.8 F, 161 UA,161 UE, 117/161UC,161Ul-1, 73, 76 F PrimaryExaminer-William D. Martin Assistant Examiner-Sadie L. ChildsAttorney-James E. Bryan [57] ABSTRACT This invention relates to aprocess for modifying the surface of a shaped article made from apolyester which comprises treating the article with an aqueous solutioncontaining a halogenated fatty acid, a wetting agent and a polymer whichis compatible with the halogenated fatty acid, and drying the treatedarticle.

1 Claim, N0 Drawings PROCESS FOR IMPROVING THE SURFACE ADHESION F SHAPEDARTICLES MADE FROM POLYESTERS This invention relates to a process formodifying the surfaces of shaped articles made from polyesters bytreatment thereof with aqueous solutions containing halogenated fattyacids and wetting agents.

Shaped articles, e.g., fibers or films, made from polyesters haveexcellent physical and chemical properties, e.g., high dimensionalstability and resistance to chemicals and solvents. The latter desirableproperty, however, entails considerable disadvantages for certainapplications. It is thus extremely difficult to apply functional layersof different chemical nature, e.g., heat-scalable layers orlight-sensitive reproduction layers, since they have an exceptionallypoor adhesion to polyester surfaces.

Various processes have been suggested to improve the adhesion of coatingto the surface of shaped articles made from polyesters. Generally, theyinclude a treatment of the surface with solutions of certain substanceswhich alter the surface physically or chemically. Simple and uniformwetting of the surface with the treating solution which is requiredtherefor could be best achieved by the use of organic solvents. It thushas been suggested to treat the surface with a solution of a halogenatedfatty acid and a resin in an organic solvent.

For the reasons of technologically substantially simpler handling andthe better obtainable adhesion of hydrophilic coatings, pretreatmentwith aqueous solutions would be preferable, however. It thus has alsobeen suggested to expose the surface to the action of concentratedsulfuric acid, if desired with the addition of oxidants, and tosubsequently wash the treated surface with water. The process inter aliahas the disadvantage that, after treatment, the sulfuric acid must becarefully removed, an additional cumbersome washing process beingrequired therefor. Furthermore, it has been suggested to use aqueoussolutions of halogenated fatty acids, e.g., trichloroacetic acid. Thetrichloroacetic acid remaining after drying can be removed relativelysimply by thermal decomposition. The process, however, has thedisadvantage that the aqueous solution does not uniformly wet thepolyester surface so that no uniform modification of the surface can beachieved. In order to overcome this drawback, wetting agents have beenadded to the treating solution. The success achieved thereby has notbeen sufficient, however, obviously because the wetting agents becomeinactive as soon as a concentrated halogenated fatty acid solutionresults during the evaporation of the water. According to anotherproposal, finely divided silica was additionally added to the solutionof halogenated fatty acid and wetting agent. This addition resulted in amarkedly more uniform modification of the surface. For certain purposes,e.g., for applying completely homogeneous, particularly hydrophilic,copying layers, further improvement of the uniformity and thus of theadhesion would be desirable. Furthermore, this process has thedisadvantage that the addition of finely distributed silica, impairs thetransparency of the finished product so that no completely clear, highlytransparent materials can be prepared therewith.

The process of the present invention modifies the surfaces of shapedarticles made from polyesters in a manner such that the application of acompletely homogeneous, uniformly firmly adhering coating is possiblewith the formation of products of high transparency.

In the present process for the modification of the surface of a shapedarticle made from a polyester, the shaped article is coated with anaqueous solution containing a halogenated fatty acid and a wetting agentand heated. Further, a dissolved or dispersed polymer is added to thesolution, which polymer is compatible with the halogenated fatty acid.

Polymers for use in the invention which are compatible with thehalogenated fatty acid in aqueous solution are those which do notprecipitate with the acid. Such precipitates may occur by the reactionof the acid with the polymer, or with the stabilizer of the dispersion,or by physical action, e.g., by salting out. The suitability of thepolymer for the purpose of the invention easily may be determined by asimple test. Preferable soluble polymers are polyacrylamide andpolyvinyl alcohol, preferable dispersed polymers are polyvinyl acetateand polyvinylidene chloride, which also may contain small quantities ofother monomeric units. Generally, it is advantageous to use a solublepolymer for pretreatment when hydrophilic coatings are to be appliedand, on the other hand, dispersions of water-insoluble polymers foranchoring hydrophobic coatings.

Particularly suitable halogenated fatty acids are the chlorinated aceticacids, e.g., trichloroacetic acid. Also, halogenated fatty acids havinglonger chains, e.g., 2,2,3-trichloropropionic acid, or fatty acidscontaining other halogen atoms, e.g., trifluoroacetic acid, may be used.The concentration of halogenated fatty acid in the pretreatment solutionmay vary within wide limits; generally it is between 5 and 20 percent byweight, preferably between 5 and 10 percent by weight. The proportion byweight of polymer to halogenated fatty acid generally is between 1:] and1:20.

Suitable polyesters having surfaces which can be modified in accordancewith the invention are all highmolecular weight condensation products ofmultivalent carboxylic acids with multivalent alcohols, which yielddeformable crystalline or partially crystalline products. Preferablyused are polyesters from terephthalic acid and ethylene glycol, butespecially copolymers of these monomers with other dicarboxylic acids,e.g., isophthalic acid, and other bior multivalent alcohols, e.g.,1,3-propanediol, 1,4-butanediol, neopentylglycol, and the like may beused.

To the pretreated shaped articles made from polyesters, there areapplied in known manner layers which are distinguished by an excellentlyuniform adhesion. Depending on the nature of the top coatings, thefinished products may be used as scalable packaging films, for example,or--after sensitizing in known manner-as transparent light-sensitivereproduction materials.

Pretreatment in accordance with the invention of shaped articles madefrom polyesters is illustrated by way of films in the followingexamples. The process, however, may be applied in the same manner toother shaped articles, e.g., fibers, and the like. All quantities statedin the examples relate to the substance contained in the solution.

polyethylene terephthalate is immersed into a solution of the followingcomposition:

100 g. of trichloroacetic acid,

10 g. of polyvinyl alcohol having a K value of 70 and free of acetylgroups (Mowiol N 70/98), l.5 g. of commercial cleansing agent,

and 890 g. of water.

+ The active constituents of the cleansing agent are a mixture ofanionic wetting agents (fatty alcohol sulfates and alkylaryl sulfonates)and non-ionic wetting agents (alkylbenzene polyglycol ether).

The film is dried for 2 minutes at 140C. in a drying cabinet. Acompletely uniform very thin layer of polyvinyl alcohol remains. Thetreated surface easily may be wetted with water, even after storage forseveral days under running water.

The film is also easily wettable when it is heated for 30 minutes to140C., for example.

To the film pretreated as described above there is applied anapproximately 10;; thick film of an aqueous solution of the followingcomposition:

The aqueous solution is adjusted to a pH value of l to 2 by means ofdiluted sulfuric acid.

The film is dried for 5 minutes at 140C. in a drying cabinet and thenmay be sensitized in known manner with aqueous solutions containinglight-sensitive substances.

The adhesion of the pigment-containing hydrophilic layer to thepretreated film is excellent. The following tests were carried out fortesting the adhesion:

A. Rub Test The film is held with both hands and rubbed to and fro forat least seconds. In the case of good adhesion, the layer does notseparate at any place from the support.

B. Adhesive Tape Test The layer was scratched by means of a testingapparatus producing grid-like incisions according to DIN (GermanIndustrial Standards) 53131, type GS 30. A pressure-sensitive adhesivetape (Tesa tape No. 104) was applied to the layer and firmly pressedthereto by rubbing the handle of scissors to and fro thereon. The tapewas then rapidly jerked back by means of its overlapping end. In thecase of excellent adhesion, the layer is not damaged.

EXAMPLE 2 For treating the surfaces of polyethylene terephthalate films,solutions of the compositions stated in the following were testedaccording to the processes stated in Example 1.

Adhesion ofthe Concentration of Proportion by weight trichloro-aceticacid Polyvinyl alcohol pigment layer acid in water (36) (Mowiol N /98):

trlchloroacetic acid 10.0 excellent 6.7 1 5 good to moderate 3.3 good tomoderate 10.0 excellent 6.7 excellent 5.0 l 10 excellent 3.3 good tomoderate l0.0 excellent 6.7 excellent 5.0 l 15 excellent 3.3 good tomoderate All solutions contained 0.15 percent of the cleansing agent ofExample 1 as the wetting agent. Concentrations of trichloroacetic acidhigher than 10 percent did not result in an improvement but rendered thepolyvinyl alcohol layers tacky.

EXAMPLE 3 7 To a film pretreated as in Example 1, there was applied afilm from a solution of the following composition:

g. of polyvinyl alcohol having a K value of 70 and containing acetylgroups (Mowiol N 70/88), 5 g. of dimethylol urea, 2 g. of sulfuric acid,and 900 g. of water.

The film was dried for 3 minutes at C. lts adhesion to the support wasexcellent according to both testing methods of Example 1.

A polyvinyl alcohol film prepared in the same manner but applied to afilm which had been pretreated only with an aqueous solution oftrichloroacetic acid and a wetting agent had no adhesion.

EXAMPLE 4 The procedure was the same as in Example 3 and the followingsolution was applied for coating:

I00 g of hydroxyethyl cellulose,

S g. of dimethylol urea, 2 g. of hydrochloric acid, 1 g. of cleansingagent as in Example 1,

and 1900 g of water.

The film was dried for 3 minutes at 120C. lts adhesion to the supportwas excellent.

A film prepared from the same solution but applied to a polyethyleneterephthalate film which had been pretreated only with an aqueoussolution of trichloroacetic acid and a wetting agent had no adhesion tothe support.

EXAMPLE 5 A p. thick biaxially stretched heat-set polyethyleneterephthalate film was coated with the following solution:

100 g. of trichloroacetic acid,

g. of polyacrylamide (Cyanamer P 250), and 900 g. of water.

The film was dried for about 3 minutes at 120C. A uniform thinpolyacrylamide film was obtained onto which a 2 percent solution of thesame polyacrylamide was cast. After drying at 120C., the polyacrylamide0 excellently adhered to the polyester film. A film of the samepolyacrylamide did not adhere to a film pretreated with an aqueoussolution containing only trichloroacetic acid and a wetting agent.

EXAMPLE 6 Two samples of a 38p. thick biaxially stretched heatsetpolyethylene terephthalate film were each coated with one of thefollowing solutions and dried for 3 minutes at 120C.

To the pretreated films there were applied 10 percent polyvinyl acetatedispersions obtained by correspondingly diluting from the dispersionsdescribed below. The films were dried for 3 minutes at 120C. and theadhesion was tested according to the methods of Example 1.

Adhesion of the polyvinyl acetate samples Precoat a b trichloraceticacid good good and Mowilith DC (I) trichloracetic acid (ll) poor poor a50 percent aqueous dispersion having a particle size of 0.5 to 5p.including polyvinyl alcohol as a protective colloid (Mowilith DN) b 50percent aqueous dispersion having a particle size of 0.5 to 3p. andincluding polyvinyl alcohol as a protective colloid (Mowilith DHN).

EXAMPLE 7 To a 38;), thick biaxially stretched and heat-set polyethyleneterephthalate film there was applied the following solution, which wasdried for 2 minutes at 120C.

I00 g. of trichloracetic acid,

30 g. of polyvinylidene chloride, added as 55 percent dispersion (Diofan230 D), 3 g. of cleansing agent as in Example I,

and

900 g. of water.

After drying, a uniform film remained which was coated with thefollowing lacquer solution:

80 g. of cellulose acetate propionate with a content of 57 percent ofpropionic acid and 3 percent of acetic acid, 500 g. of acetone, and 500g. of methyl ethyl ketone.

The lacquer was dried for 3 minutes at 110C. The remaining film had athickness of about 8p. and adhered excellently to the support. A film ofcellulose acetate propionate which was cast onto a film pretreated onlywith trichloroacetic acid had no adhesion or only moderate adhesion whenits adhesion was tested according to the methods of Example 1.

EXAMPLE 8 The following solutions were applied to a 75p. thick biaxiallystretched and heat-set film of polyethylene terephthalate. Drying wasthen carried out for 2 minutes at 120C.

of trichloroacetic acid,

of polyvinyl acetate, added as 55 percent dispersion having a particlesize of 0.3 to 2p. and including polyvinyl alcohol as a protectivecolloid (Mowilith DM of polyvinylidene chloride, added as 55 percentdispersion in water (Diofan 230 D),

of anionic wetting agent (straightchain alkylaryl sulfonate), and

of water.

After drying, a uniform film remained to which the following lacquersolution was applied.

80 g. of cellulose acetate propionate having a content of 57 percent ofpropionic acid and 3 percent of acetic acid, 500 g. of acetone, and 500g. of methyl ethyl ketone.

The approximately 8 .1, thick lacquer layer adheres excellently to thesupport. When applying a corresponding layer to a similar filmpretreated, however, only with trichloroacetic acid, the celluloseacetate propionate does not adhere or has only a moderate adhesion,tested according to the methods of Example 1.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

l. A process for modifying the surface of a shaped article made from apolyester which comprises treating the article with an aqueous solutioncontaining a halogenated fatty acid, a wetting agent, and a polymerselected from the group consisting of polyacrylamide and polyvinylalcohol, and drying the treated article.

